1. Field of Endeavor
The present invention relates to ultraviolet radiation and more particularly to an ultraviolet radiation detector and dosimeter.
2. State of Technology
Intense, acute and recurrent ultraviolet radiation (UVR) exposure can be hazardous to men and women working or recreating in areas of high levels of solar UVR. Although thermal effects and resulting heat related injuries, direct damage to the exposed skin and the development of various skin cancers are among the most widely recognized of the harmful effects, other less well-understood effects of UVR exposure have also been identified. Studies indicate that UVR exposures at environmental levels suppress immune responses in both rodents and humans, resulting in enhanced susceptibility to infectious diseases including influenza and herpes. These impacts of UVR exposure represent potentially serious threats to the ability of workers to meet the demands of involving outdoor activities. In addition, non-work (recreational) activities frequently involve exposure to solar radiation.
To effectively assess the impacts of UVR exposure, an individual UV dosimeter capable of measuring and recording both UVA and UVB exposure over extended periods of time is an essential need. The use of a tried and proven UVA/B dosimeter capable of monitoring the levels of individual UVR can be an important tool in studies to evaluate direct impacts on individuals such as skin burning (erythema), carcinogenesis, and impacts to cellular immunity. New state-of-the-art advances in solid state UV detector technology have made it possible to construct a rugged, reliable, economical, and reusable device by which to measure UV exposure.
Some of the requirements for a personal ultraviolet dosimeter include the capability to measure and record UV dose rate and accumulated dose during entire deployment period for study individuals. The device must measure and record both UVA (320-400 nm) and UVB (280-320 nm) radiation with appropriate spectral sensitivity, operational flexibility and convenience.
In the past, considerable effort has been expended to develop a variety of different UV dosimeter technologies. Two paths have been considered; one, based on photosensitive film materials, and the other based on the response of photoelectric materials. In the case of photosensitive film-based sensors such as polisulphon film, the principle that is leveraged is that of photo-degradation of sensitive materials. Such detection systems have proven to have good sensitivity, but because of the operating principle, they have the disadvantages of not being reusable, being incapable of prolonged accumulation of data and exhibiting certain difficulties in providing quantitative measurements. For these reasons, detectors based on this principle are not considered suitable to meet emerging field study needs.
The second type of UV sensor, based on photoelectric response of materials, is more commonly used in modern digital instruments and is more suitable to long time-scale field studies. The photosensitive elements of most modern UV sensors are semiconductor photo-detectors—either photo-resistors or potential barrier structures. Photo-resistors have high photosensitivity, but they cannot operate in the electro-generator mode and have non-linear dependence of the photocurrent on radiation flux density. Therefore, the better approach to development of modern photo-detectors has been the creation of potential barrier structures, which: (i) have high impedance; (ii) can operate at high frequencies; and (iii) are compatible with microchip technologies. Especially attractive are Schottky diodes, because the short-wave UV radiation is absorbed in the region with a high electric field, and this substantially increases the response speed (up to 109 s) and quantum efficiency (up to 70-80%).